The present invention relates to an internal combustion engine with at least one turbocharger consisting of a turbine and of a compressor whose compressor is connected by way of a charging pressure line to a suction manifold of the internal combustion engine and whose turbine is connected into an exhaust gas line coming from an exhaust gas manifold and in which a controllable blow-off valve (waste gate) is installed into a by-pass line by-passing the turbine and coming from the exhaust gas manifold while the compressor is adapted to be short-circuited by way of a vent valve.
By equipping internal combustion engines with exhaust gas turbochargers, it is possible to gain back at least a part of the lost energy present in the exhaust gases and to feed the same back to the internal combustion engine. However, as the supercharged air quantity supplied by the exhaust gas turbocharger and therewith the charging pressure assumes sufficient values only with a larger exhaust gas flow (i.e , at higher values of engine load and engine rotational speed and additionally increases strongly with increasing exhaust gas flow, the charging pressure has to be regulated and/or controlled for attaining a good dynamic behavior of the internal combustion engine and for avoiding its destruction.
This takes place as a rule by a pneumatically controlled blow-off valve (by-pass valve) which is acted upon by the charging pressure and is located in a by-pass channel (by-pass) with respect to the turbine of the exhaust gas turbocharger and thus reduces the exhaust gas flow through the turbine at excessively high charging pressures.
If, however, an output control device (throttle valve) of the internal combustion engine is suddenly no longer actuated at relatively high load, for example, for changing a driving point (transmission speed) of a motor vehicle equipped with this internal combustion engine, then a pressure shock occurs upstream of the throttle valve because the exhaust gas turbocharger at first continues to supply charging air; as a result thereof, devices in the suction path of the internal combustion engine such as, for example, throttle valve or air-quantity measuring device may be destroyed under certain circumstances. In order to avoid this, it was proposed in the DE-OS No. 32 46 483 to open the blow-off valve with a closed throttle valve.
However, this entails the disadvantage that the rotational speed of the turbocharger decreases strongly during the transition into the coasting operation, for example, during the change of the driving point so that the energy lost therewith is missing for the re-acceleration of the internal combustion engine after completed change of the driving point.
It is therefore the object of the present invention to far-reachingly avoid a loss of kinetic energy in an exhaust gas turbocharger of an internal combustion engine during the transition into the coasting operation and nonetheless to reliably protect the internal combustion engine inclusive all of its auxiliary aggregates against overload due to excessively high charging pressures.
The underlying problems are solved according to the present invention in that the blow-off valve is activated into the closed condition at least for a limited time interval during the transition of the internal combustion engine into the coasting operation.
The advantages of the present invention reside in the first instance in that during the transition into the coasting operation a loss of kinetic energy of the exhaust gas turbocharger is far-reachingly avoided during the transition into the coasting operation by the activation of the blow-off valve into its closed condition. By including an atmospheric air valve in a by-pass to the compressor which opens at vacuum in the suction manifold of the internal combustion engine and at excessively high charging pressures, pressure shocks in the suction path of the internal combustion engine are additionally dampened.